Sizing the helm (iron man )

Hey guys .
Im new here as most of the other posts I have seen hehe and in dire need of some help..

Ive started to make iron man mark6 suit. only cod, legs and shoes left.
In foam that is, but I wanna do the helm in pepa kura resin ect, so I can keep it for display/ nightlight xD

so I was wondering.. when U scale/size it, it there any way u can measure ur head or something and run by the numbers in pepkura,for exaple height wihththth( dunno how to spell it ), diametre or something .

Or it it just by guessig.
270mm hmmm seeems more or less. and then when its finished, DOh it doest fit :S

on another note, Love this forums and Keep it up every 1 , stealth, demo, robo, indiefilmgeek ect ect awesome work keep inspiering ppls ^^

A lot of people measure their head but don't add the extra inch or so that the helmet needs so it can slip over your head and around your ears. Now, everyone has a differently shaped head, so this might not work for everybody but like broadway said, look in the mirror and measure the height of your head, from chin to the top of your dome, then add 25mm to that, or an inch if you use inches. I don't use the width measurement because it always comes out too big, but the height usually works awesome.

After that just make sure that the helmet is correct in the way it's setup, then just scale the height and the width and depth scale automatically.